Subscriber backpressure

A subscriber can control events in its queue to avoid any overruns. It can also request more events if there is additional capacity. Backpressure enforces the publisher to bound the event queues according to the subscriber. Furthermore, a subscriber can ask to receive one element at a time, building a stop-and-wait protocol. It can also ask for multiple elements. On the other hand, a publisher can apply the appropriate buffers to hold non-delivered events, or it can just start to drop events if the production rate is more than the consumption rate.

It is important to note that the Reactive Streams API is aimed at the flow of events between different systems. Unlike ReactiveX, it does not provide any operators to perform transformations. The API has been adopted as a part of the java.util.concurrent.Flow package in JDK 9.